Pumps for supplying hydraulic fluid to a power steering motor of a vehicle are known. Further, controls for controlling the output of a power steering pump are known. At high vehicle speeds, minimum steering assist is required. Thus, relatively low pressure and flow rates are required from the power steering pump. At low vehicle speeds, greater assist is desirable than at high vehicle speeds. Thus, at low vehicle speeds higher pressure and flow rates are required than those at high vehicle speeds. When maximum assist is required, such as during parking on dry pavement, maximum pressure is required from the power steering pump.
Obviously, it is desirable to have an ultra-compact power steering pump capable of producing the pressure needed to operate the power steering motor for performing steering maneuvers at the different vehicle speeds. Many hydraulic pumps have been developed over the years for use in power steering systems and/or for other uses.
One such pump, known as a gear pump, has a plurality of internal fluid pumping chambers formed between teeth of a gear set. The gear pump has a first gear element which rotates about a fixed axis and a second gear element which rotates about an axis disposed eccentrically from the fixed axis. The gear teeth on the first and second gear elements define pumping chambers. Rotational motion between the first and second gear elements causes one set of pumping chambers to expand and a second set of pumping chambers to contract. Kidney-shaped ports are positioned adjacent the rotating gear members and overlie the rotating gear members such that one kidney-shaped port is in continuous communication with the set of expanding pumping chambers and the other kidney-shaped port is in continuous communication with the set of contracting pumping chambers.